REGIONAL ANAESTHESIA




Most foot and ankle surgery is performed in the day care setting. A combination of regional or field block with or without general anaesthesia allows faster patient recovery and better postoperative analgesia. Following are the different blocks used in foot and ankle surgery.


POPLITEAL BLOCK


Popliteal block will essentially block two terminal branches of the sciatic nerve. It has to be combined with saphenous nerve block for completeness of block technique.


Indication


Surgery on ankle or foot. If a tourniquet is required, a calf tourniquet should be used. This block can be used as the sole anaesthetic or in conjunction with general or spinal anaesthesia for postoperative analgesia.


Contraindications




  • 1.

    Patient refusal


  • 2.

    Infection at the site of block


  • 3.

    Coagulopathy



Precaution


It will cause foot drop, which may delay mobilisation or discharge of the patient.


Surgery on the forefoot can be easily performed under an ankle block. Popliteal block in these cases is not necessary.


Anatomy


The predominant nerve innervating the lower limb below the knee is the sciatic nerve and its branches. The saphenous nerve is the only sensory contribution below the knee from the femoral nerve.


The sciatic nerve divides at a variable distance proximal to the popliteal crease into tibial and common fibular ( peroneal ) nerves.


The saphenous nerve is given out from the posterior division of the knee, and it travels with femoral artery deep to the sartorius. It becomes superficial posterior and lateral to the knee joint and then travels the leg along with the great saphenous vein.


The nerves can be identified using a nerve stimulator or, more easily, using ultrasound.


Nerve stimulator-guided technique


Although various approaches to the nerves in popliteal fossa have been described, the preferable one is the posterior approach. This approach is less painful to the patient as the needle passes only through skin and fat on its way to the nerves.


Equipment and drugs




  • 1.

    Nerve stimulator (e.g., B Braun stimuplex)


  • 2.

    Insulated 50 mm needle


  • 3.

    Local anaesthetic. Use 0.5% levobupivacaine for anaesthesia and 0.25% if the block is done only for postoperative analgesia



Procedure


See Figure 10 .




Fig. 10


After intravenous access is established and appropriate monitoring applied, the patient lies in a prone position. A pillow is placed underneath the patient’s leg so that the knee is slightly flexed. A line is drawn along the popliteal crease. Along this line, the tendon of biceps is felt on the lateral side of the fossa and marked. Similarly, the tendon of semitendinosus is felt on the medial side and marked. The line between these tendons is divided into half. A perpendicular line is drawn to this line cephalad. A point on this perpendicular line is marked 7 cm from the popliteal crease. Needle insertion point is 1 cm lateral to this point.


An intradermal wheal of local anaesthetic is injected at this point. A 5 cm stimulating needle is then inserted perpendicular to skin. The initial stimulating current is set at 1 mA, frequency 2 Hz. Nerve stimulation should be elicited within 1.5–2.5 cm. With this approach, the common fibular ( peroneal ) nerve is often first identified, causing dorsiflexion of the foot. Once the needle is adjusted so that a twitch may be found at 0.3–0.5 mA, 10 ml of local anaesthetic is injected after excluding intravascular needle placement by careful aspiration. The twitch should disappear immediately. The needle should then be re-directed to stimulate the second nerve. It should be either moved medially to find the tibial nerve (if the common fibular ( peroneal ) nerve was found first) or laterally to find the common fibular ( peroneal ) nerve (if the tibial nerve was found first).


Once the other nerve is located, another 10 ml of local anaesthetic is injected.


Complications




  • 1.

    Nerve damage


  • 2.

    Intravascular injection leading to local anaesthetic toxicity





Ultrasound technique


Popliteal block can be safely and easily done using ultrasound. Indications and contraindications are similar to nerve stimulator-guided nerve block.


Equipment and drugs




  • 1.

    Ultrasound machine with high-frequency linear probe


  • 2.

    Probe cover and jelly


  • 3.

    Nerve stimulator (e.g., B Braun stimuplex)


  • 4.

    Insulated 100 mm needle


  • 5.

    Local anaesthetic. Use 0.5% levobupivacaine for anaesthesia and 0.25% if the block is done only for postoperative analgesia



Procedure


After intravenous access is established and appropriate monitoring used, the patient lies supine with leg supported and resting on a chair. See Figures 11 and 12 .




Fig. 11



Fig. 12


Probe is placed behind the knee just above the popliteal crease so that a cross-sectional view of the popliteal artery is obtained. Vein is identified superior to it. Nerves are superficial to the blood vessels. The tibial nerve is identified initially. The common fibular ( peroneal ) nerve is seen to approach the tibial nerve when probe is moved cephalad. Once the nerves are identified, a needle is inserted in the plane so that the entire needle is visualised as it approaches the nerve. Twenty ml of local anaesthetic is injected to surround the nerves.


Complications of this procedure are similar to nerve stimulator-guided procedure.




ANKLE BLOCK


This is a simple block to do that targets the terminal branches of the sciatic and femoral nerves.


Indications




  • 1.

    It can be used as an anesthetic technique for surgery on the forefoot.


  • 2.

    It can be used for postoperative analgesia for surgery on the midfoot done under general anaesthesia, since most of these types of surgery need a thigh tourniquet.



Contraindications




  • 1.

    Patient refusal


  • 2.

    Infection at the site of block


  • 3.

    Coagulopathy



Complete ankle block requires five injections. Mild sedation, therefore, may improve patient comfort during block performance.


Anatomy


There are five nerves to block. The tibial, superficial, deep fibular ( peroneal ), and sural are branches of sciatic nerve. The saphenous nerve arises from the femoral nerve.


See Figure 8 on page 122 and Figures 18 and 19 on page 129 for sensory innervation of the ankle.


Aug 10, 2019 | Posted by in ORTHOPEDIC | Comments Off on REGIONAL ANAESTHESIA
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